1. Field of the Invention
The present invention relates generally to semiconductor fabrication, and more particularly to an apparatus and method for removing particles from a surface.
2. Description of Related Art
Removal of sub-100 nanometer (nm) particles from a surface can be a challenging subject for semiconductor fabrication processes. The surface-particle interactions depend on the material and the surface structure and generally are size independent. To remove a particle from a surface, the adhesive forces between the particle and the surface need to be broken and the particle needs to be transported far enough away from the surface so that the particle will not be redeposited on the surface.
Currently, semiconductor technology uses reflective optics which requires a surface roughness of approximately 1.5 Angstrom RMS. However, the incident light is scattered by the rough surfaces and it leads to the loss of intensity of the reflected light and image deformation. Hence, the conventional wet cleaning techniques that uses under etching of particle to remove it from the surface no longer are applicable.
Other examples for removing particles from a surface include transferring of energy to a particle, where the energy transfer efficiency to a particle on a surface strongly depends on the size of the particle on the surface. However, this method can only be used to remove “soft” defects, where particles like particle 10A that adhere to surface 12A due to van der Waals and electrostatic forces, as illustrated in FIG. 1A. It is much more difficult to remove particles (e.g., particles 10B) that are chemically bonded to a surface (e.g., 12B), known as “hard” defects, shown in FIG. 1B.
Another example for removing particles uses cryogenic cleaning. A jet of material, which may include some type of cleaning particle 14, may be expelled from the cryogenic cleaner and the transfer energy from jet to the contaminant particles 10C, as shown in FIG. 2. However, the cryogenic process makes it difficult to produce a narrow distribution of particle sizes, which makes it very difficult to remove smaller contaminant particles from the surface. Referring to FIG. 3, larger cleaning particles, such as cleaning particle 14A in a distribution will not be able to remove smaller particles 10D from surface 12D. Further, the use of larger cleaning particles can cause damage to the surface, making it impossible to achieve a surface roughness of 1.5 Angstroms RMS.
The referenced shortcomings are not intended to be exhaustive, but rather are among many that tend to impair the effectiveness of previously known techniques concerning surface cleaning; however, those mentioned here are sufficient to demonstrate that the methodologies appearing in the art have not been satisfactory and that a significant need exists for the techniques described and claimed in this disclosure.